1. Field of the Invention
This invention relates to fasteners, and particularly to surgical fasteners used to join body tissue.
2. Description of the Prior Art
Fasteners have been used surgically to eliminate the need for suturing, which is both time consuming and inconvenient. In many applications the surgeon can use a stapler apparatus, i.e., a fastener implanting device loaded with surgical fasteners to accomplish in a few seconds what would have taken many minutes to perform by suturing. This reduces blood loss and trauma to the patient. The terms "fastener" and "staple" are used interchangeably herein.
Surgical fasteners have been in the form of ordinary metal staples, which are bent by the delivery apparatus to hook together body tissue. Also, two-part fasteners have been used, as illustrated in U.S. Pat. No. 4,506,670 in which a barbed staple is used in conjunction with a retaining piece to hold the staple in place.
Typically, the two part staple comprises a back span and two barbed prongs which are engaged and locked into a separate retainer piece. In use, the staple is pressed into the body tissue so that the barbs penetrate the tissue and emerge from the other side where they are then locked into the retainer piece. The retainers prevent the staple from working loose from the tissue. The two piece fasteners cannot be unlocked and are not removable. For this reason, they must be made of a bioabsorbable material.
Korthoff, et al., U.S. Pat. No. 4,667,674, herein incorporated by reference, discloses a two part surgical fastener comprising a fastener member and a retainer member. The fastener member has a base, and a pair of prongs extending perpendicularly from the base. The prongs are spaced inward from the respective ends of the base in order to prevent splaying of the prongs, and to improve hemostasis.
The two piece fasteners require the staple delivery apparatus to have access to both sides of the tissue. Usually, such devices have a U-shaped member into which tissue is inserted. The stapler apparatus has a fastener holder and an anvil which are pivotally connected at one end, and mounted on the legs of the U-shaped support structure. See, for example, Green U.S. Pat. No. 4,402,445, which discloses a surgical fastener and means for applying same. In a surgical operation, the issue to be joined is positioned between the fastener holder and the anvil, which contains the fastener retainers. The fasteners are ejected from the holder into the tissue, and the prongs are locked into the retainers.
In some applications, however, it is not possible to have access to body tissue from two opposite directions. For example, in skin grafting applications one can only apply fasteners from a stapler positioned above the skin.
The prior art includes many examples of surgical staplers which do not enclose the body tissue between an anvil and fastener holder. For example, surgical staplers such as those described in U.S. Pat. No. 3,643,851 and U.S. Pat. No. 4,618,086 approach the skin from one direction. However, they require the use of staples which are malleable enough to be crimped by an anvil so that the prongs hook into the tissue. Typically, such staples are made of metal and are not bioabsorbable. They must be removed by another device, such as a stapler extractor. Furthermore, such staples are useful for joining tissue layers laterally, as for example in closing wounds in skin or fascia, but are not optimum for laminarly fastening one layer of tissue onto another, as in skin grafting.
Hence there is a need for a surgical fastener which is capable of being delivered into the surface of body tissue from one direction, which can join layers of tissue both laterally and laminarly as required in skin grafting applications, and which is bioabsorbable to eliminate the need for a separate and painful removal operation.